A military term. Refers to rooting through an assortment of items and only taking what you want/need. It usually involves opening up a package or something shrinkwrapped, taking the desired item(s) and leaving the rest behind for the next unsuspecting individual.

Term is used in the Infantry division of the Army when someone opens up an MRE (meal ready to eat) package and only takes the candy/cookies. This leaves the next person to a meal with no treat.

"Some asshole ratfucked my MRE and took the Tootsie Pop!"

"Who ratfucked the Costco potato chip assortment and only took the Doritos?"

"You dick. You ratfucked the mini-cereals and only took the Apple Jacks".